1. Field of the Invention
The present invention relates generally to the field of ultrasonic imaging and therapeutic treatment of the vascular anatomy, and particularly for the construction and use of guiding catheters used in accessing the vascular anatomy. More particularly, the invention relates to the rotational correlation of intravascular ultrasonic images produced within such guiding catheters with the vascular orientation of the guiding catheters.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in peripheral blood vessels that feed the limbs of the body and coronary blood vessels that feed the heart. When deposits accumulate in localized regions of the blood vessels, blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty, where a balloon-tipped catheter is used to dilate a stenosed region within the blood vessel; placement of a stent for maintaining vessel patency after angioplasty; atherectomy, where a blade or other cutting element is used to sever and remove the stenotic material; and laser angioplasty, where laser energy is used to ablate at least a portion of the stenotic material.
In order to more effectively introduce such interventional devices into the vascular anatomy, and particularly into the coronary vasculature, a guiding catheter is generally employed. The guiding catheter is inserted percutaneously into the patient's arterial system, usually by a percutaneous puncture made in the femoral artery in the groin. With the aid of a guidewire (and usually with the assistance of fluoroscopy), the guiding catheter is advanced upwardly through the patient's aorta to the coronary ostia. Usually, the distal end of the guiding catheter is specially shaped to facilitate placement of the distal tip of the guiding catheter against the ostium of one of the coronary arteries and to maintain the guiding catheter in place throughout the procedure. The shape of the distal end allows the distal end of the guiding catheter to point into the ostium, with the catheter body being buttressed against the opposite wall of the aorta.
Once the guiding catheter is in place, therapy proceeds by introducing a therapeutic catheter or other interventional device through the guiding catheter and to the desired treatment location within the coronary arteries. Before employing the therapeutic catheter, however, it is often necessary to properly locate the diseased region of the vessel as well as the position (including the orientation) of the therapeutic catheter relative to the diseased region so that the interventional element on the therapeutic catheter can be employed to treat the diseased region. Directional devices, such as directional atherectomy catheters can be "aimed" at the disease to selectively remove tissue. One approach for visualizing the interior of the vessel is by intravascular ultrasound (IVUS) where a catheter having an ultrasonic imaging element is introduced beyond the guiding catheter and into the vessel to produce cross-sectional images of the vessel. Ultrasonic imaging catheters may also include an interventional element so that therapy can occur without exchanging the imaging catheter for an interventional catheter after imaging has occurred. For example, in the case of atherectomy procedures, one common approach is to employ an imaging catheter having a cutting element located inside of canoe-shaped housing. On the backside of the housing is a low pressure balloon which is inflated to force the atherosclerotic tissue into the opening of the housing and into the path of the cutter for subsequent removal. Often, the atherosclerotic buildup is only on one side of the vessel wall, commonly referred to as eccentric plaque, thereby making it desirable to position the housing so that the cutting blade is directed only against the eccentric plaque and not the healthy vessel wall. One proposed method for positioning the cutting blade is to rotate the proximal portion of the catheter (which is outside of the patient) until the opening in the housing is aimed at the diseased portion of the vessel. The balloon is then inflated and the cutter is advanced within the housing to shave away the atherosclerotic tissue.
While such ultrasonic images of the vessel assist in locating the existence of the plaque, it has heretofore been difficult to precisely correlate the orientation of the cross-sectional images produced by the imaging catheter with the actual spatial orientation of the image feature within the blood vessel. Many imaging catheter constructions provide no information at all relative to the rotational orientation of the imaging catheter within the blood vessel while the image is being produced. In such cases, correlation of the image with the actual orientation of the blood vessel is difficult or impossible.
It would therefore be desirable to provide improved catheters and methods which would facilitate correlation of an ultrasonic cross-sectional image with the physical orientation of the catheter producing such an image within the coronary vasculature. In this way, regions of the blood vessel requiring therapy can be precisely located and targeted for subsequent interventional treatment. Further, it would be particularly desirable if the rotational orientation of the imaging catheter could be uniquely determined while within the guiding catheter so that the orientation of the imaging catheter can be correlated with the real time ultrasonic image being produced. Most preferably, such improvements should require only modifications of proven catheter designs so that the other functions of the catheters are subsequently undisturbed.
2. Description of the Background Art
A variety of patents describe vascular guiding catheters, including U.S. Pat. Nos. 4,817,613; 5,163,921; and 5,318,032.
U.S. Pat. No. 5,054,492 describes an ultrasonic imaging catheter having both an ultrasonically opaque element and a fluoroscopic marker on the catheter body. Both markers are employed to determine the actual rotational orientation of the catheter within the body lumen being viewed.